You can find examples in such mods as: Area 51, Piratez, Final Mod Pack, X-Com Files.
I could post some examples here, but it's exactly the same syntax as Hobbes' example.
Or, if you are using OXCE+, you can use a random list:
- name: CAVES_01
width: 20
length: 20
randomizedItems:
- position: [12, 15, 2]
amount: 1
mixed: true
itemList: [STR_SKULL, STR_SPIDERWEB, STR_SPIDERWEB, STR_SPIDERWEB, STR_OLD_HANDBAG, STR_OLD_BOOT, STR_SHIV, STR_BONE, STR_BIG_BONE]
In this example, one item is taken at random from the list.